One place where I worked spend a lot on ads, but they also hired some marketing people and a leads conversion person who seemed to be able to quantify how much return on investment they were getting from ads.
Thing is, everybody involved has an interest in making the numbers look good. And it's really easy to make them look good even without faking anything. Just omit the fact that you're counting post view leads, stretch the lookback window, etc
I think he did a bit more of an objective job than that. He compared platforms where we were advertising and I remember that Pinterest generally gave a far better return on investment (than Facebook, which was the main platform we used).
